The development of electronic products, such as cellular phones, computers and cameras, is towards smaller and smaller devices. The physical size of the devices should lessen as should their cost, which put high demands on, among other things, the layouts of integrated circuits required in the products, and the fabrication methods used for producing them.
The shielding of integrated circuit packages against electromagnetic interference (EMI) effects should also be made in as cost effective way as possible, while not compromising the quality requirements. Shielding is utilised for several reasons, a first reason being the fulfillment of government regulatory specifications, e.g. ETSI (European Telecommunications Standards Institute) specifications that for example put limits to allowed harmonics. Another reason for utilizing shielding is to provide immunity from other interfering wireless sources nearby, and yet another reason is to assure proper operation of a wireless transceiver itself by preventing transmission of non-intended radiation, such as from internal circuitry. Shortly, shielding is utilized in order to eliminate or at least minimize the effects of electromagnetic radiation.
There is a number of different ways to achieve shielding of an integrated circuit or electronic module. A commonly used solution is to mount a metallic hood to the module, for example by soldering. This however entails several drawbacks. A major drawback is the inflexibility of the fabrication process in that new tooling has to be provided in the production line for each change made to the module design. Another drawback is that the building height, i.e. the vertical height of the module increases, which of course is quite contrary to the wish of providing miniaturised modules and components. Further, the shielding efficiency is lessened due to holes in the metal, holes through which a moulding compound protecting the die is to be passed, or holes used for improving the inspectability of the module. Still further, the metallic hood constitutes an additional component to be manufactured and subsequently mounted on the module. Further yet, the mounting of the metallic hood also requires an extra space around the circuitry, for example in order to accomplish the soldering of the hood, again in contrary to the general goal towards smaller devices.
Another way to accomplish shielding of a module is to flip the package upside down and use the upper PCB copper plane as the shielding. However, this entails a more complex PCB (printed circuit board) and also an extra space requirement for accommodating solder balls of a ball grid array (BGA), if such surface-mount packaging is used. Further, this solution shows a very poor heat transfer performance and the heat dissipation for cooling the die is thus a major shortcoming.
Yet another way that has been contemplated for providing a shielding to a module is to integrate the shielding in the moulding compound, the moulding compound having a special composition containing absorbing/conductive fillers for absorbing and conducting the radiation, respectively. Further, the electrical performance of the device may also be affected by introducing such fillers. This solution would therefore probably be a very expensive solution involving substantial research and development costs.